The Supreme Court just shut down a major tech controversy: police planting a GPS bug without your knowledge or the approval of a judge. By a unanimous decision, the court said such warrantless tracking is illegal. This is big.

The case originated with a Maryland drug dealer whose car was nailed with a GPS tracker—and installed after the ten day window originally permitted by a warrant. Before he was caught, the dealer's coordinates were relayed to police for almost a month, without any judicial oversight. The Obama White House had previously claimed this was fair game, as driving your car on public roads in plain view abandons any expectation of privacy.

Not so fast, says the Supreme Court:

The Fourth Amendment protects the "right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures." Here, the Government's physical intrusion on an "effect" for the purpose of obtaining information constitutes a "search." This type of encroachment on an area enumerated in the Amendment would have been considered a search within the meaning of the Amendment at the time it was adopted.

Here, physical contact means "putting a GPS device on your car"—and under the law, has the same weight as the police kicking down your door. A physical search—something cops can't generally do unless a judge says so.

Wired is hailing the ruling as "arguably the biggest Fourth Amendment case in the computer age," and we're inclined to agree. But as Justice Alito notes, there are plenty of unresolved issues unwrapped here:

The Court's reliance on the law of trespass will present particularly vexing problems in cases involving surveillance that is carried out by making electronic, as opposed to physical, contact with the item to be tracked. For example, suppose that the officers in the present case had followed respondent by surreptitiously activating a stolen vehicle detection system that came with the car when it was purchased. Would the sending of a radio signal to activate this system constitute a trespass to chattels?

When a centuries-old document tries to wrangle things like GPS and radio waves, there will be problems. Luckily, we have one fewer problem as of today. You can read the decision in its entirety below. [Wired]